Cut any of the loops of strings below and the whole chain comes apart.
You will find many of these kinds of puzzles in my book “Impossible Folding Puzzles and Other Mathematical Paradoxes” .
Elementary 4-manifold topology
Thébault’s theorem
If you place squares on the sides of any parallelogram, their centers will always form a square.
Geometric Illusion: Vertigo Pattern
Do you feel queasy when you look at this wallpaper? Though they appear to be sloped, the columns of stacked white and black patterns are perfectly straight and PARALLEL to each other.
Interested in my optical illusions? Feel free to visit my author page.